Molded plastic container with reduced neck ovality

ABSTRACT

A plastic container has a main body portion, a neck portion and a molded feature such as an anti-rotation lug adjacent to the neck portion. The molded feature has a volume that is less than a volume that would be defined by the maximum external dimensions of the feature. This reduces the shrinkage differential between the molded feature and the neck portion, which could otherwise cause sealing problems with a closure as a result of deformation of the neck portion. A method of correcting a sealing problem in a plastic container by reducing the volume of the molded feature is also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.13/246,967 filed Sep. 28, 2011, which is incorporated by referenceherein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to the field of packaging, and morespecifically to molded plastic containers of the type that have neck orfinish portion that is constructed and arranged to form a seal withrespect to a closure.

2. Description of the Related Technology

Plastic containers are typically fabricated using either injectionmolding or one of two types of blow molding. The blow molding process ischaracterized by using internal pressure to force a hot, soft plasticpreform or parison against a molding surface. Blow molding can beperformed using either a reheat stretch blow molding process, which istypical for plastic containers that are fabricated from polyethyleneterephthalate (PET), or an extrusion blow molding process, which istypical for containers that are fabricated from such materials ashigh-density polyethylene and polyolefins.

In the extrusion blow molding process, a molten tube or parison iscontinuously extruded from an extrusion fixture. A mold assembly thatmoves at a speed that is substantially equal to the speed of theextruded parison periodically captures portions of the parison, andpressurization as applied to inflate the captured portion of the parisonagainst the interior surfaces of the mold assembly. The mold assembly istypically mounted for motion on either a molding wheel, which moves in acircular path, or on a shuttle, which moves the mold assembly on asubstantially straight path.

Plastic containers typically include a neck or finish portion having anopening that is in communication with the interior space of thecontainer. In some instances, the neck or finish portion is threaded topermit application of a closure. In other cases, structure is moldedinto the neck or finish portion to permit a closure to be snapped on.The neck or finish portion typically includes at least one sealingsurface that is adapted to bear against a portion of a closure in orderto form a liquid tight seal with respect to the closure when it isproperly applied.

As is shown in FIGS. 1 and 2, one type of conventional plastic container10 includes a main body portion 12 and a neck portion 14. The neckportion 14 has an upper lip 16 that defines an opening and a sealingsurface 18 that is constructed and arranged to form a seal with respectto an applied closure. A molded feature such as an anti-rotation lug 20is provided adjacent to the neck portion. The anti-rotation lug 20 had agenerally triangular shape when viewed in side elevation, with a firstinclined side surface 24, a second inclined side surface 26 and a solidouter surface 22 facing away from the neck portion 14. It had a maxim umwidth W₁, a maximum height H₁ and a maximum radial depth D₁. Theanti-rotation lug 20 functioned to prevent or deter a closure from beingunscrewed from the neck portion 14 by a consumer after it has beenapplied by the manufacturer. In the case of such containers, theanti-rotation lug 20 was integral with the neck portion 14 at a part ofthe neck portion 14 that was nearby the sealing surface 18.

Some of these containers 10 experienced a deformation condition known asovalization, in which the neck or finish portion 14 deviated from itsideal substantially cylindrical shape. This created sealing problemswith respect to an applied closure. The inventors herein have identifieda cause of such ovalization as being uneven shrinkage of the neck orfinish portion after the hot molded container is removed from the mold.It has been determined that the thermal mass of the anti-rotation lugwas a significant factor in causing the uneven shrinkage.

A need exists for an improved molded plastic container having a neck orfinish portion that is adjacent to a molded feature that is lesssusceptible to deformation as a result of uneven cooling after thecontainer has been removed from the mold. A need also exists for amethod of correcting a sealing problem in such a container that iscaused at least in part by the presence of the molded feature.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the invention to provide an improvedmolded plastic container having a neck or finish portion that isadjacent to a molded feature that is less susceptible to deformation asa result of uneven cooling after the container has been removed from themold.

It is further an object of the invention to provide a method ofcorrecting a sealing problem in such a container that is caused at leastin part by the presence of the molded feature.

In order to achieve the above and other objects of the invention, aplastic container that is constructed according to a first aspect of theinvention includes a main body portion having an inner surface thatdefines an interior space. The container further includes a neck portionhaving an opening that is in communication with the interior space. Inaddition, the container includes a molded feature that is adjacent tothe neck portion. The molded feature has a space defined therein so thatit occupies a volume that is less than a volume defined by the maximumexternal dimensions of the molded feature, whereby distortion of theneck portion as a result of differential cooling during the fabricationprocess is reduced.

A method of correcting a sealing problem in a plastic container having amain body portion defining an interior space, a neck portion defining anopening and having a sealing surface that is designed to seal withrespect to a closure and a molded feature that is integral with the neckportion according to a second aspect of the invention includes steps ofidentifying a sealing problem that is created by differential shrinkageof the molded feature with respect to another portion of the container;and reducing the volume of the molded feature with respect to a volumethat is defined by the maximum external dimensions of the moldedfeature.

These and various other advantages and features of novelty thatcharacterize the invention are pointed out with particularity in theclaims annexed hereto and forming a part hereof. However, for a betterunderstanding of the invention, its advantages, and the objects obtainedby its use, reference should be made to the drawings which form afurther part hereof, and to the accompanying descriptive matter, inwhich there is illustrated and described a preferred embodiment of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary front elevational view of a portion of aconventional plastic container having a molded feature adjacent to aneck portion;

FIG. 2 is a fragmentary side elevational view of a portion of theconventional container that is shown in FIG. 1;

FIG. 3 is a fragmentary front elevational view of a portion of a plasticcontainer that is constructed according to a first embodiment of theinvention;

FIG. 4 is a fragmentary side elevational view of a portion of theplastic container that is shown in FIG. 3;

FIG. 5 is a fragmentary front elevational view of a portion of a plasticcontainer that is constructed according to a second embodiment of theinvention;

FIG. 6 is a fragmentary side elevational view of another portion of theplastic container that is shown in FIG. 5;

FIG. 7 is a diagrammatical depiction of the volumetric reduction that isaccomplished in a molded feature in the different embodiments of theinvention; and

FIG. 8 is a flow chart depicting a method that is performed according toa preferred embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Referring now to the drawings, wherein like reference numerals designatecorresponding structure throughout the views, and referring inparticular to FIG. 3, a plastic container 30 according to a firstembodiment of the invention includes a main body portion 32 that has aninner surface that defines an interior space and a neck portion 34having an opening defined by an upper lip 36 that is in communicationwith the interior space. A sealing surface 38 is provided in the neckportion 34 for providing a seal with respect to a closure.

The plastic container 30 is preferably fabricated from a plasticmaterial such as high-density polyethylene using an extrusion blowmolding process. Alternatively, the plastic container 30 could befabricated from a material such as polyethylene terephthalate (PET)using a reheat stretch blow molding process. As another possiblealternative, plastic container 30 could be fabricated using injectionmolding.

Referring again to FIG. 3, it will be seen that plastic container 30includes a molded feature 40 that is adjacent to the neck portion 34. Inthis embodiment, the molded feature 40 is an anti-rotation lug 42 thathas a generally triangular shape when viewed in side elevation. Theanti-rotation lug 42 includes a first side portion 44, a second sideportion 46, with the first and second side portions 44, 46 beingseparated by an upper opening 48 that is embodied as a slot that extendssubstantially radially.

The anti-rotation lug 42 preferably has a maximum width W₂, which is themaximum external dimension of the molded feature 40. It further has amaximum height H₂ and a maximum radial depth D₂.

The anti-rotation lug 42 further preferably has a first portion 52, bestshown in FIG. 4, which is integral with the neck portion 34 and a secondportion 54 having an outer surface 55 that faces radially outwardly. Acavity 49 is defined within the anti-rotation lug 42. The cavity 49 ispreferably defined in the outer surface 55 of the second portion 54.

Because of the presence of the cavity 49 and the opening 48, the moldedfeature 40 occupies a volume that is less than a volume that wouldotherwise be defined by the maximum external dimensions of the moldedfeature 40. In addition, the surface area of the molded feature 40 issubstantially increased relative to what it would have been in the eventthat the molded feature 40 was solid plastic, as was the molded featurein the conventional container that is described above with respect toFIGS. 1 and 2. As a result, the molded feature 40 will cool and shrinkwhen removed from the mold at a rate that is more similar to adjacentstructure, such as the neck portion 34, it would be the case if therewere solid. Accordingly, distortion of the sealing surface 38 isminimized.

The anti-rotation lug 42 further preferably is shaped so as to have amaximum wall thickness T₂, best shown in FIG. 7, which is definedbetween the cavity 49 and the respective outer surfaces of the first andsecond side portions 44, 46.

A plastic container 60 according to a second embodiment of the inventionis depicted in FIGS. 5 and 6. it includes a main body portion 62 thathas an inner surface that defines an interior space and a neck portion64 having an opening defined by an upper lip 66 that is in communicationwith the interior space. A sealing surface 68 is provided in the neckportion 64 for providing a seal with respect to a closure.

The plastic container 60 is preferably fabricated from a plasticmaterial such as high-density polyethylene using an extrusion blowmolding process. Alternatively, the plastic container 60 could befabricated from a material such as polyethylene terephthalate (PET)using a reheat stretch blow molding process. As another possiblealternative, plastic container 30 could be fabricated using injectionmolding.

Referring again to FIG. 5, it will be seen that plastic container 60includes a molded feature 70 that is adjacent to the neck portion 64. Inthis embodiment, the molded feature 70 is an anti-rotation lug 72 thathas a generally triangular shape when viewed in side elevation. Theanti-rotation lug 72 includes a first side portion 74, a second sideportion 76, with the first and second side portions 74, 76 beingseparated by an upper opening 78 that is embodied as a slot that extendssubstantially radially. The first and second side portions 74, 76 arethinner than those in the first embodiment described above, and theopening 78 is larger.

The anti-rotation lug 72 preferably has a maximum width W₃, which is themaximum external dimension of the molded feature 40. It further has amaximum height H₃ and a maximum radial depth D₃.

The anti-rotation lug 72 further preferably has a first portion 82, bestshown in FIG. 6, which is integral with the neck portion 64 and a secondportion 84 having an outer surface 85 that faces radially outwardly. Acavity 79 is defined within the anti-rotation lug 72. The cavity 79 ispreferably defined in the outer surface 85 of the second portion 84.

As a result of the presence of the cavity 79 and the opening 78, themolded feature 70 occupies a volume that is less than a volume thatwould otherwise be defined by the maximum external dimensions of themolded feature 70. In addition, the surface area of the molded feature70 is substantially increased relative to what it would have been in theevent that the molded feature 40 was solid plastic, as was the moldedfeature in the conventional container that is described above withrespect to FIGS. 1 and 2. As a result, the molded feature 70 will cooland shrink when removed from the mold at a rate that is more similar toadjacent structure, such as the neck portion 64, it would be the case ifthere were solid. Accordingly, distortion of the sealing surface 68 isminimized.

The anti-rotation lug 72 further preferably is shaped so as to have amaximum wall thickness T₃, which is defined between the cavity 79 andthe respective outer surfaces of the first and second side portions 74,76.

Preferably, a ratio of the volume occupied by the molded features 40, 70to the volume defined by the maximum external dimensions of therespective molded features 40, 70 is substantially within a range ofabout 0.1 to about 0.8, more preferably substantially within a range ofabout 0.2 to about 0.7, and most preferably substantially within a rangeof about 0.3 to about 0.6.

Preferably, a ratio of the maximum wall thickness T₂, T₃ to the maximumexternal dimension of the molded feature 40, 70 is substantially withina range of about 0.05 to about 0.45, more preferably substantiallywithin a range of about 0.1 to about 0.35 and most preferablysubstantially within a range of about 0.2 to about 0.3.

The presence of the cavity 49, 79 and the opening 48, 78 also causes asubstantial increase in external surface area of the anti-rotation lug42 relative to what it would have been without those features.Preferably, this increase in surface area is substantially at leastabout 10%.

A preferred method of correcting a sealing problem in a plasticcontainer of the type described above with respect to the twoembodiments of the invention is shown diagrammatically in FIG. 8. Itincludes steps of identifying a sealing problem that is created bydifferential shrinkage of the molded feature with respect to anotherportion of the container, and reducing the volume of the molded featurewith respect to a volume that is defined by the maximum externaldimensions of the molded feature.

The step of reducing the volume of the molded feature is preferablyperformed by conducting a mold tooling change, and more specifically byrevising the shape of the molded feature to include a cavity.

It is to be understood, however, that even though numerouscharacteristics and advantages of the present invention have been setforth in the foregoing description, together with details of thestructure and function of the invention, the disclosure is illustrativeonly, and changes may be made in detail, especially in matters of shape,size and arrangement of parts within the principles of the invention tothe full extent indicated by the broad general meaning of the terms inwhich the appended claims are expressed.

What is claimed is:
 1. A method of correcting a sealing problem in aplastic container having a main body portion defining an interior space,a neck portion defining an opening and having a sealing surface that isdesigned to seal with respect to a closure and a molded feature that isintegral with the neck portion, comprising steps of: identifying asealing problem that is created by differential shrinkage of the moldedfeature with respect to another portion of the container; and reducingthe volume of the molded feature with respect to a volume that isdefined by the maximum external dimensions of the molded feature.
 2. Amethod of correcting a sealing problem according to claim 1, wherein thestep of reducing the volume of the molded feature is performed byconducting a mold tooling change.
 3. A method of correcting a sealingproblem according to claim 1, wherein the step of reducing the volume ofthe molded feature is performed by revising the shape of the moldedfeature to include a cavity.
 4. A method of correcting a sealing problemaccording to claim 3, wherein the cavity has an opening that faces in adirection that is substantially opposite from the neck portion.
 5. Amethod of correcting a sealing problem according to claim 1, wherein themolded feature comprises an anti-rotation lug.